I can only imagine the reason it wasn't released was the Blue Note founders wont to not dilute the market by releasing too much from one artist too close together. It's why a bunch of stuff was shelved.
The book is Notes and Tones by Arthur Taylor. You may know Arthur as the great jazz drummer, but he had the incredible foresight to conduct interviews with a bunch of his fellow musicians and record them for posterity. He was able to get very candid conversations out of them because he was a friend and one of them. I’ve only read the Blakey chapter, but it really is great. Check the list of interviews:
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